A human perceives sound as a result of collection of external sound by the pinna and transmission of the sound to the tympanic membrane through the external auditory canal. In a human, auditory sense gives an effect on his/her concentration and attentiveness. It is known that increasing auditory sensitivity, for example, by enhancing a sound collection effect leads to enhancement of concentration and attentiveness (Patent Literature 1). Also, there is known a headphone-type sound collector capable of effectively collecting a voice coming from the front (Patent Literature 2).